During last century, society became increasingly aware of and sensitized to environmental questions, and more particularly to the ecological effects of the use of chemicals in industry. This has led to an increase in the use of biodegradable products such as nontoxic biodegradable surfactants, for example. Surfactants based on sugars obtained from renewable resources represent a good solution to this need since they possess good surface-active properties. Their use as emulsifiers in the food industry and in polymerization reactions has been documented, for instance in detergents, cosmetics and surface cleaning products. Two broad categories of surfactants based on carbohydrates are now being marketed: carbohydrate-based fatty acid esters, and alkyl (poly)glycosides. The carbohydrate-based fatty acid esters are only stable over a limited range of pH, as they are hydrolyzed in acid or alkaline conditions. In contrast, the alkyl (poly)glycosides are very stable in alkaline conditions, but they are sensitive in an acid environment. The alkyl polyglycosides (APGs) are the best known in this category.
In the category of carbohydrate-based fatty acid esters, the esters of fatty acids and of sorbitol (SFAEs), of sorbitan (1,4-anhydrosorbitol), of isosorbide (1,4-3,6-dianhydrosorbitol) or of sucrose are among the nonionic surfactants that are the most readily available commercially. However, surfactants having an ester function are not stable in acid and basic conditions. To rectify this problem, the inventors proposed replacing the ester bond with an ether functionality to improve the stability of these species. However, preparation of derivatives of ethers based on carbohydrates generally requires the use of expensive and/or toxic solvents (dimethylsulfoxide, dimethylformamide, dimethylacetamide), high temperatures or steps of protection/deprotection, the use of nonrecyclable reagents, of strong bases (such as sodium or potassium hydroxide or sodium hydride), or the use of reducing agents that produce waste products or need to be hydrolyzed at the end of the reaction (such as sodium, aluminum or boron hydrides; hydrosilanes and hydrosiloxanes).
In this context, the inventors recently reported, in French patent application No. 14/01346, an efficient method of synthesis of sugar ethers by hydrogenolysis of the corresponding sugar acetals. In fact, the inventors have developed a process for synthesis of sugar ethers, with or without solvent, by a first step of acetalization or trans-acetalization using a catalyst and a second step of reduction of the sugar acetals by hydrogenolysis to obtain a mixture of regioisomers of sugar ethers. These two steps were optimized without purification of the acetal intermediates in order to reduce the overall cost of the process.
In order to obtain, at good yield, a composition having high and stable surface-active properties notably by employing a process that satisfies the industrial, economic and environmental constraints, the inventors suggested that this process could be employed for obtaining a composition of long-chain sugar ethers.
However, the inventors found that this process is not suitable for a step of acetalization using a long-chain alkyl aldehyde. In fact, when long-chain alkyl reagents are used, low yields are obtained.
There is therefore a need for a process that is economical and environmentally friendly for producing an environmentally friendly composition that has high surface-active properties that are stable over time and in the face of variations of pH.
After much experimentation, the inventors succeeded in finding a solution to the aforementioned problems. Thus, the inventors developed, for the first time, a novel route for the synthesis of long-chain alkyl saccharide monoethers having characteristics of surfactants. In fact, the inventors showed that a better yield in the synthesis of long-chain alkyl saccharide acetals can be obtained using a short-chain alkyl aldehyde as co-reactant. The inventors have developed an efficient process for the synthesis of long-chain alkyl saccharide monoethers having characteristics of surfactants using a reducing agent that does not produce any waste products (such as hydrogen) at the end of the reaction compared to other methods of ether synthesis using hydrides as the reducing agent. The process for synthesis of long-chain alkyl saccharide monoethers as proposed by the inventors can be carried out using only biosourced reactants, which are or can be synthesized from renewable raw materials (such as fatty aldehydes, which may be prepared from fatty acids, or saccharides or polyols that are obtainable from starch). The inventors have also developed a process for synthesis of long-chain alkyl saccharide monoethers comprising a reaction sequence involving two acetalization reactions and one hydrogenolysis reaction, without the need for a step of purification of the crude mixture of sugar acetals. Finally, the inventors have developed an economical, efficient and environmentally friendly means for synthesizing compositions of alkyl saccharide monoethers comprising long chains or short chains, these compositions of saccharide ethers displaying improved properties of surface tension and surface-active properties similar to those of long alkyl chain surfactants alone. The inventors have demonstrated a synergistic effect between the surfactants with short and long alkyl chains providing both a decrease in the surface tension of water and an increase in solubility of the long alkyl chain surfactant in aqueous solution.
EP 0 019 999 A1 describes the preparation of long-chain alkyl saccharide acetals, in particular of sorbitol partially substituted with acetate groups from C7-C30 aldehydes preferably comprising a 70:30 mixture of C12/C14 alkyl chains and of acetic acid as the reaction mixture.
Fanton E. et al.: “Long-chain acetals derived from sucrose as a new class of surfactants”, Carbohydrate Research, Pergamon, GB, Vol. 298, No. 1-2, 20 Feb. 1997, pages 85-92, describes the preparation of C6-C18 higher alkyl acetals of acetylated sucrose starting from the corresponding aldehydes.
WO 2012/148530 describes compositions of monoalkyl ethers of polyols and more particularly of mono-anhydrohexitol having a C4-C18 alkyl ether radical.